Wearable devices and systems are beneficial as eye measurements using a platform close to one or both eyes reduces measurement errors generated by head movements and other sources. Historically, wearable applications have been limited to the realms of research, opthamologic surgery, and military because of the limitations associated with wearable eye-tracking devices. Wearable systems tend to be bulky and expensive due to the inconvenience of the required camera location. Custom, difficult to manufacture imaging and illumination systems are required to achieve unobtrusive form factors. Gaze mapping and/or gaze determination may be data and computationally intensive resulting in limited real-time functionality if the system is not tethered to a computer. Finally, one method of attaining higher accuracy is to control the presence of glints in terms of location and intensity in the eye image. As a result, outdoor functionality is significantly limited by noise in the form of extraneous glints. Extraneous glints are generally caused by sources of light (direct or indirect) external to the system.
An example is the reflection of the scene in a user's eye captured in the eye image. For a similar reason, eye-tracking systems that rely on Purkinje images for gaze determination are often incompatible with glass and contact wearers.